It is common practice in the foundry art to form cores and molds in desired shapes from a sand-resin composition which can be cured at foundry room temperatures. Typically, a granular aggregate such as sand is combined with a minor amount of a polymerizable resin sufficient to act as a binder when the resin on the sand is polymerized with an initiator for the resin.
More particularly, foundries currently use processes comprising gas-curing a foundry sand mixed with a wide variety of polymerizable resins which are cured with one or more of numerous curing agents. The preparation of cores and molds using such processes is taught in U.S. Pat. Nos. 3,008,205; 3,108,340; 3,121,368; 3,145,438; 3,639,654; and 3,879,339 (hereafter "'339" for brevity) inter alia. Though these prior art cores and molds have gained varying degrees of commercial acceptance, each has certain drawbacks. Some cores and molds are difficult to form into average patterns, or require an uneconomically long period of time for curing them; others have inferior tensile strength and other undesirable characteristics such as a proclivity to generate surface cracks; yet other are impractical because they use a binder which is too unstable to be commercially profitable; in addition to one of the foregoing drawbacks cores and molds may have still others which are less serious.
It is of particular interest that no prior art reference suggests that an acid-curable resin may be cured by gassing with sulfur dioxide (SO.sub.2) without the formation of sulfuric acid. Several references indicate that it essential to generate sulfur trioxide as a precursor of the sulfuric acid, and in the '339 patent Richard teaches the formation of sulfuric acid without the formation of sulfur trioxide, but no reference teaches the curing of a furan resin without the formation of sulfuric acid. Nor does any reference teach that it would be desirable that the structure of the cured or polymerized resin should be modified by chemically incorporating therewithin an aralkyl initiator moiety with an alkyl substituent on the ring, which moiety inculcates highly desirable characteristics into the polymerized resin of the cured core or mold.
This invention is specifically directed to a novel process in which a sand-furane resin mixture containing a minor amount of diisopropylbenzene monohydroperoxide (DIPBMHP) or diisopropylbenzene dihydroperoxide (DIPBDHP) substantially homogeneously intermixed in the resin, is cured by gassing with sulfur dioxide in such a way that an intermediate acid sulfate is formed instead of sulfuric acid, and the DIPBMHP or DIPBDHP moiety becomes chemically bound in the polymer formed. The resulting cured resin binds the sand to provide a core or mold of exceptional strength because of the unique properties of the resin containing a DIPBMHP or DIPBDHP moiety.
Particularly referring to the '339 patent, Richard discovered that by employing sulfur dioxide in combination with an oxidizing agent it was possible to generate sulfuric acid in situ without forming sulfur trioxide. Because of this process it was possible to cure an acid curing resin in a period of a few seconds to a few minutes at ambient temperatures while obtaining homogeneous products with high flexural strengths. Specifically with respect to a furane or furane copolymer type resin optionally modified by furfuryl alcohol or by unsaturated epoxidized compounds, Richard teaches that polymerization of the resin is effected by alkyl or aralkyl hydroperoxide, hydrogen peroxide, alkyl peroxides such as methylethylketone peroxide or t-butyl hydroperoxide, and the specific alkaryl hydroperoxide, cumene hydroperoxide. With the use of each of these oxidizing agents there results the direct formation of sulfuric acid without the formation of sulfur trioxide. From the mechanisms and theoretical considerations delineated in the '339 patent, it is clear that formation of sulfuric acid contraindicates the formation of an acid sulfate of the hydroperoxide, which acid sulfate could then generate a carbonium ion to initiate the polymerization of the resin and then become chemically bound in its structure. Neither DIPBMHP or DIPBDHP reacts with the sulfur dioxide in the manner disclosed by Richard; nor is an analogous polymerized end product formed.